Ubiquitous network access has been almost realized today. From network infrastructure point of view, different networks belong to different layers (e.g., distribution layer, cellular layer, hot spot layer, personal network layer, and fixed/wired layer) that provide different levels of coverage and connectivity to users. Because the coverage of a specific network may not be available everywhere, and because different networks may be optimized for different services, it is thus desirable that user devices support multiple radio access networks on the same device platform. As the demand for wireless communication continues to increase, wireless communication devices such as cellular telephones, personal digital assistants (PDAs), smart handheld devices, laptop computers, tablet computers, etc., are increasingly being equipped with multiple radio transceivers. A multiple radio terminal (MRT) may simultaneously include a Long-Term Evolution (LTE) or LTE-Advanced (LTE-A) radio, a Wireless Local Area Network (WLAN, e.g., WiFi) access radio, a Bluetooth (BT) radio, and a Global Navigation Satellite System (GNSS) radio.
Due to spectrum regulation, different technologies may operate in overlapping or adjacent radio spectrums. For example, LTE/LTE-A TDD mode often operates at 2.3-2.4 GHz, WiFi often operates at 2.400-2.483.5 GHz, and BT often operates at 2.402-2.480 GHz. Simultaneous operation of multiple radios co-located on the same physical device, therefore, can suffer significant degradation including significant coexistence interference between them because of the overlapping or adjacent radio spectrums. Due to physical proximity and radio power leakage, when the transmission of data for a first radio transceiver overlaps with the reception of data for a second radio transceiver in time domain, the second radio transceiver reception can suffer due to interference from the first radio transceiver transmission. Likewise, data transmission of the second radio transceiver can interfere with data reception of the first radio transceiver.
FIG. 1 (Prior Art) is a diagram that illustrates interference between an LTE transceiver and a co-located WiFi/BT transceiver and GNSS receiver. In the example of FIG. 1, user equipment (UE) 10 is an MRT comprising an LTE transceiver 11, a GNSS receiver 12, and a BT/WiFi transceiver 13 co-located on the same device platform. LTE transceiver 11 comprises an LTE baseband module and an LTE RF module coupled to an antenna #1. GNSS receiver 12 comprises a GNSS baseband module and a GNSS RF module coupled to antenna #2. BT/WiFi transceiver 13 comprises a BT/WiFi baseband module and a BT/WiFi RF module coupled to antenna #3. When LTE transceiver 11 transmits radio signals, both GNSS receiver 12 and BT/WiFi transceiver 13 may suffer coexistence interference from LTE. Similarly, when BT/WiFi transceiver 13 transmits radio signals, both GNSS receiver 12 and LTE transceiver 11 may suffer coexistence interference from BT/WiFi. How UE10 can simultaneously communicate with multiple networks through different transceivers and avoid/reduce coexistence interference is a challenging problem.
FIG. 2 (Prior Art) is a diagram that illustrates the signal power of radio signals from two co-located RF transceivers. In the example of FIG. 2, transceiver A and transceiver B are co-located in the same device platform (i.e., in-device). The transmit (TX) signal by transceiver A (e.g., WiFi TX in ISM CH1) is very close to the receive (RX) signal (e.g., LTE RX in Band 40) for transceiver B in frequency domain. The out of band (OOB) emission and spurious emission resulted by imperfect TX filter and RF design of transceiver A may be unacceptable to transceiver B. For example, the TX signal power level by transceiver A may be still higher (e.g. 60 dB higher before filtering) than RX signal power level for transceiver B even after the filtering (e.g., after 50 dB suppression).
In addition to imperfect TX filter and RF design, imperfect RX filter and RF design may also cause unacceptable in-device coexistence interference. For example, some RF components may be saturated due to transmit power from another in-device transceiver but cannot be completely filtered out, which results in low noise amplifier (LNA) saturation and cause analog to digital converter (ADC) to work incorrectly. Such problem actually exists regardless of how much the frequency separation between the TX channel and the RX channel is. This is because certain level of TX power (e.g., from a harmonic TX signal) may be coupled into the RX RF frontend and saturate its LNA. If the receiver design does not consider such coexistence interference, the LNA may not be adapted at all and keep saturated until the coexistence interference be removed (e.g. by turning off the interference source).
Various in-device coexistence (IDC) interference mitigation solutions have been proposed. Moving the ISM band signal away from the LTE licensed band is one possible IDC solution. For example, an in-device BT module may apply adaptive frequency hopping (AFH) to adjust the frequency hopping range. An in-device WiFi module may select another WiFi access point (AP) that operates in another frequency channel farther away from the LTE band. Those solutions, however, cannot work properly unless the BT module can successfully complete initial connection setup, or unless the WiFi module can successfully scan WiFi beacons from other WiFi APs. Additional solutions are sought to protect BT/WiFi connection setup or other important signaling procedures.